jesliwoo,
Hello again! I have good news and bad news:
The good news: A 3.5 GPA is fine, even for the top schools! Why do you feel it is sub-par? Is there a particular academic area or course you did not do well in that you'd like to improve? Taking an extra class in a field you did not do especially well, is the ONLY reason to take a side course.
The bad news: Taking a side course or two will not move the needle on your application. It is not the same as dealing with the pressures and rigor of an undergraduate experience.
You should instead use the time you have off to put together a strong application with regards to your essays, resume, and letters of recommendation. If you're not applying for a while, then try to work on an extracurricular activity or something else that will help round out your profile.
If you would like to discuss in greater detail, at
Admissionado we offer Advanced Planning Programs and other forms of mentorship to help aspiring MBAs build out their profiles in preparation for their applications.
https://admissionado.com/free-consultation/Best,
Seth